1. Field of the Invention
This invention relates to a liquid crystal display, and more particularly to a method and apparatus for adaptively reducing picture quality deterioration caused by a dithering in a liquid crystal display panel.
2. Description of the Related Art
Generally, in a liquid crystal display (LCD) a picture is displayed by controlling the light transmittance of the liquid crystal having a dielectric anisotropy. To this end, the LCD includes a liquid crystal display panel having a pixel matrix, and a driver for driving the liquid crystal display panel.
Specifically, as shown in FIG. 1, the LCD includes a liquid crystal display panel 12 having a pixel matrix 10, a gate driver 12 for driving gate lines GL1 to GLm of the liquid crystal display panel, a data driver 14 for driving data lines DL1 to DLn of the liquid crystal display panel, and a timing controller 16 for controlling driving timings of the gate driver 12 and the data driver 14.
The liquid crystal display panel includes a pixel matrix 10 consisting of pixels formed for each area defined by intersections between the gate lines GL and the data lines DL. Each of the pixels includes a liquid crystal cell LC for controlling a light transmission amount in accordance with a pixel signal, and a thin film transistor TFT for driving the liquid crystal cell LC.
The thin film transistor TFT is turned on when a gate-on voltage (VGH) from the gate line GL is supplied, to thereby supply a pixel signal from the data line DL to the liquid crystal cell LC. Further, the thin film transistor TFT is turned off when a gate-off low voltage (VGL) from the gate line GL is supplied, to thereby keep a pixel signal charged in the liquid crystal cell LC.
The liquid crystal cell LC can be expressed equivalently as a capacitor Clc. The equivalent capacitor consists of a common electrode opposed to a pixel electrode connected to the thin film transistor TFT, and a liquid crystal between the electrodes. Furthermore, the liquid crystal cell LC includes a storage capacitor (not shown) so as to stably keep the charged pixel signal until the next pixel signal is charged. Gray scale levels are achieved by controlling light transmittance of the liquid crystal cell. The light transmittance is controlled by changing the alignment state of the liquid crystal having a dielectric anisotropy in accordance with the pixel signal charged through the thin film transistor TFT, as discussed below.
The gate driver 12 shifts a gate start pulse (GSP) from the timing controller 16 in response to a gate shift clock (GSC) (not shown) to thereby sequentially apply a scanning pulse having the gate-on voltage (VGH) from a power supply (not shown) to the gate lines GL1 to GLm. The gate driver 12 applies a gate-off voltage (VGL) from the power supply to the gate lines GL to GLm in the remaining interval during which a scanning pulse having the gate-on voltage (VGH) is not applied. Such a gate driver 12 controls the width of the scanning pulse in response to a gate output enable signal (GOE) from the timing controller 16.
The data driver 14 shifts a source start pulse (SSP) from the timing controller 16 in response to a source shift clock (SSC) to generate a sampling signal. Further, the data driver 14 latches pixel data (RGB) inputted in accordance with the source shift clock (SSC) in response to the sampling signal and thereafter applies the latched sampling signal line by line in response to a source output enable signal (SOE). Then, the data driver 14 converts the pixel data (RGB) applied line by line into analog pixel signals using gamma voltages from a gamma voltage part (not shown) to apply them to the data lines DL to DLm. The data driver 14 then determines a polarity of the pixel signal in response to a polarity control signal (POL) from the timing controller 16 when the pixel data are converted into the pixel signals. The data driver 14 determines the time interval at which the pixel signals are applied to the data lines DL in response to the source output enable signal (SOE).
The timing controller 16 generates signals, for example, GSP, GSC and GOE, to control the gate driver 12 and signals, for example, SSP, SSC, SOE and POL, to control the data driver 14. The timing controller 18 generates the control signals using a data enable signal DE which indicates an effective data interval inputted from the exterior, a horizontal synchronizing signal Hsync, a vertical synchronizing signal Vsync and a dot clock DCLK which determines the transmission timing of the pixel data RGB.
A liquid crystal display (LCD) having the above-mentioned configuration employs a dithering method using a frame rate control algorithm (FRC), hereinafter referred to as “FRC dithering”, in order to increase the gray level. The FRC dithering method divides a pixel in a picture field into a certain size of dithering blocks to control pixel brightness within the blocks and to differentiate the pixel brightness within the block for each frame. Accordingly, the FRC dithering method allows a larger number of gray levels to be displayed than the predetermined number of gray levels displayable without dithering.
When the FRC dithering method is used for an LCD in which one pixel can display 18-bit colors by a combination of R, G, and B data, it can obtain an effect similar to a case in which 24-bit colors arc displayed by a combination of the R, G, and B data, each of which has 8 bits. The FRC dithering function is generally built in a scaler IC of a computer or a timing controller of the LCD. Thus, the scaler IC makes a FRC dithering process of an input data to transmit it to the LCD capable of displaying 18-bit colors, or to transmit 24-bit R, G, and B data to the LCD in which the FRC dithering function is built.
However, there is a disadvantage with the FRC dithering process when it is utilized in an LCD driven by a vertical 2-dot inversion system. More specifically, the FRC dithering process is applied to specific patterns, for example, a dot pattern or a vertical stripe pattern, the FRC dithering process deteriorates the picture quality by introducing a flicker, noise, and/or dark bar into the displayed picture.